Seems Blackmagic had done something to their video capture setup (Desktop Video 12.0 and above, Windows 10) but the phenomenon happens only in Vegas! (all versions).
On import these files to Vegas you get only the video track without the audio track. Doing the same to Premier, Resolve, WMP - the audio is there. Double clicking the video in Windows - it plays video and audio. Inspecting the file properties in the Windows explorer it states video AND audio tracks (24bit 48000Hz) but inspecting the same file in Vegas it states Video at the correct values and Audio as 00:00:00:00 means no audio/no sync... and it does not play or present itself in the timeline.
Have any of you experienced that?
BTW, importing older files plays well as normal - but only the latest drivers and software support the 4K Declink Card